1. Technical Field
The present invention relates to a cassette-type chemical sample treatment system apparatus and method for use in the treatment of less than one milligram quantities of amino acids, proteins, peptides, and the like pursuant to predetermined or preselected chemical, biochemical, and biomedical protocols. More particularly, the invention of this application relates to a cassette-type chemical sample treatment system and method having a cassette for holding a plurality of sample columns for immobilizing preselected samples and a plurality of reagent wells for retaining preselected reagents for enabling predetermined chemistries of the preselected samples with the preselected reagents, including column loading, treatment, and post-treatment analysis of the reacted sample with near-zero dead volume and minimal human intervention, the predetermined chemistries being specified by machine readable code integrated into the cassette.
2. Background Art
With the exception of certain high-performance liquid chromatography (HPLC), proteins and peptides are typically fractionated in aqueous buffers containing amines, salts and, often, denaturants. Therefore, additional manipulations such as desalting by HPLC, precipitation, or dialysis are required to render the sample matrix compatible with protein and peptide chemistry or peptide sequencing protocol. Each of these additional steps, however, involves potential losses, especially when only less than milligram amounts of protein are present at low concentrations. It is generally understood that proteins include peptides, accordingly, for purposes of this invention, no distinction is made between peptides and proteins, and reference to one will also apply to the other.
Many of the steps involved with the aforementioned steps have been eliminated by immobilizing a protein or a peptide directly onto a solid support, washing away any interfering components, and leaving the protein bound to the support ready for either further on-column chemistries or removed for analysis. Hewlett-Packard Analytical Instruments (Palo Alto, Calif., US) manufactures a family of analytical devices (HP-G1000A, HP-G1004B, and HP-G1005A) which use sample columns containing a solid support upon which proteins or peptides might be immobilized. The HP-G1004A is a Protein Chemistry Station (PCS) which permits on-column chemistries to proteins and peptides immobilized on a hydrophobic support. The HP-G1005 performs standard Edman degradation protocols on a peptide immobilized on a bi-phasic support for the performance of peptide sequencing.
Post-translational modifications will determine the stereochemistry and conformation of the peptide. Accordingly, there is a need to determine the nature of the side groups so that a conformational analysis or a structure determination may be made. Such post-translational modification chemistries may be carried out manually or semi-automatically whereby a sample is subjected to reaction with the appropriate reagents to give an appropriate indication in the event the post-translational modification is present. The HP-G004 Protein Chemistry Station (PCS) represents the state of the art with respect to enabling semi-automatic performance of chemistries. The PCS has limitations, however, with respect to the types and complexity of chemistries that might be performed on this system. For example, the PCS is not able to perform bi-directional pumping; it can only pump down. This limitation precludes shuttling sample or reagents back and forth through the support. This feature would be desirable, for example, when the reactivity of a side group is affected by the polarity of a solvent and the appropriate solvent is one that may separate the sample from the support. Second, the chemistries performed in the PCS require that the reagents be dispensed into a large funnel in order to be introduced to the reaction. Without changing-out the funnel between reagents, a significant risk of cross-contamination is created.
The HP PCS system employs a hydrophobic column to immobilize the sample during loading and during application of the chemistry. FIG. 1 is a cross-sectional diagram of single sample reaction chamber typical of the background art. A funnel a is press-fit attached to the inlet side of the hydrophobic column b, with the throat of the funnel c in communication with the top opening of the column d. The funnel/column assembly is loaded into a center cavity e of a clear Lucite reaction chamber f, the assembly being secured by compressing and twisting the funnel/column assembly in a single movement into a bayonet-type connection on the walls of the Lucite holder g, and the column being urged against the funnel by a spring k. A cap h is screwed onto the reaction chamber so as to seal the system. Inlet ports i,j in the cap permit the introduction of sample into the funnel and the introduction of a pressurized inert gas to pump the reagent through the column. During the chemistries performed on the PCS, the funnel is never changed-out. As a result, a serious concern with the system and method of the background art is that the side walls of the funnel may retain residues of previously introduced reagents, thus resulting in cross-contamination or reagents.
After insertion and bayonet-locking of the funnel/column assembly into the reaction chamber, a protein or peptide solution sample is loaded in the 5 ml funnel attached to the column. The cap is screwed onto the holder and over the funnel so that pressurized nitrogen, or other inert gas, may be applied to the sample and pressure forced into and through the hydrophobic sample column. The sample loading process captures proteins and peptides on the hydrophobic portion of the sample column, while the sample solvent passes through.
It is possible to do multiple sample additions for larger volumes or to use a second solution to wash the sample. First, the holder cap removed, and a second sample or aqueous wash is added to the funnel, the cap reattached to the holder, and the holder pressurized with nitrogen, thus forcing the aqueous wash through the hydrophobic sample column.
Following the sample loading, sample preparation (rinses), and possible sample pre-treatment, the funnel/column assembly is removed from the sample reaction chamber and is transferred to another reaction chamber in the Protein Chemistry Station, wherein the appropriate reagents are administered to perform the desired chemistries. A technician selects a computer program which directs the PCS, via a micro-controller interface, to dispense the appropriate reagent into the sample funnel pursuant to the selected program. The appropriate reagent is directed through a tube and into a reagent port in the cap of the reaction chamber. The reagent flows from the reagent port into the sample funnel. Pressurized inert gas then forces the reagent out of the sample funnel and into the column.
All chemistries are carried out in the column or the funnel, and within the reaction chamber. Also, since only one reaction chamber may be loaded at a time in the PCS, preparation and treatment of multiple sample columns is a time consuming and tedious effort. Further, the PCS provides only four reservoirs for reagents, buffers or solvents, all of which must be a liquid. Additionally, there may be reactions, especially of biomedical interest, wherein a solid reagent, such as a lyophilized enzyme, vaccine, hormone preparations, and the like which exhibit lower stability in solution, tending to either degrade rapidly or require low storage temperatures in its hydrated state, may be needed in order to execute the desired chemistry. The devices of the background art are not able to accommodate these dry reagents. Accordingly, there is a need for an automated chemical treatment system capable of performing a multiplicity of both peptide and post-translational modification chemistries sequentially on a plurality of samples, in an uninterrupted manner with minimal human intervention or direction. The automated chemical treatment system would also provide means to perform chemistries external to the sample columns and for reintroduction of the reacted sample or analyte to the sample column. Also, there is a need for an automated system that would provide means for "just-in-time" delivery of reagents requiring just-in-time solubilization, such as adsorbed, lyophilized or other powdered reactants to the sample.
Since the same sample funnel is used for all reagents there is a risk of cross-contamination that may affect the outcome of sensitive chemistries. Minute quantities of reagent may adhere to the walls of the funnel, only to be eluted into the sample column when the next reagent is introduced into the funnel. Where less than one milligram quantities of peptides or proteins are being investigated, the presence of minute amounts of impurities or cross-contaminants may have a significant impact on the results. Accordingly, there is a need for a sample column/reaction chamber system that permits near-zero dead volume to minimize risk of cross contamination and the resulting inaccuracies such contamination may cause.
Once the protein chemistries are complete, the sample column from the PCS is removed from the sample reaction chamber and is transferred to the appropriate analytical measurement device in order to measure or characterize the results of the chemistries performed. Typically, the analysis is selected to characterize the products of a peptide cleavage.
Typically, RP-HPLC is used to analyze the reaction products. Ideally, it would be desirable to insert the sample column of background art directly into an HPLC sample column holder, thus integrating the sample column into the HPLC and transforming the sample column into a RP-HPLC column. In order to obtain adequate separation of proteins, however, column pressures greater than 1500 psi are required. The sample column of the background art rated to withstand pressures up to approximately 1000 psi. At pressures greater than 1000 psi, the non-tapered end of the sample column typically fails. In order to operate at the extremely high pressures required for protein separation, a special adapter is required, and is attached to the inlet end of the sample column to accommodate a high pressure line fitting. FIG. 2 shows a cross-section diagram of the sample column and adapter typical of the background art. The adapter 1 is inserted into the non-tapered end d of the sample column b. Since the sample column is a pre-column to the chromatography column of the HPLC, the adapter is also a part of the HPLC pre-column. Accordingly, the column plus adapter of the background art is supplied in addition to the standard chromatogragh column rather than as a substitute column. Consequently, the adapter 1 must also be packed with a hydrophobic support m, and once it is affixed to the outlet end d of the hydrophobic column, becomes an extension of the original hydrophobic column upon which the sample is immobilized. As a result, the adapter may be used only once and then must be discarded. Accordingly, there is a need for a sample column able to withstand the high pressures of RP-HPLC that might be directly incorporated, without an adapter or modification, into an HPLC receptacle so as to integrate the sample column as the chromatography column of the RP-HPLC.
The above single-sample procedures associated with the current state of the art device are incapable of performing chemistries or sequential, uninterrupted treatment of multiple samples and results, therefore, in extremely tedious protocols and prone to cross-contamination. Further, a well recognized problem associated with the incorporation of the hydrophobic column into the RP-HPLC is that the coupling between the inlet port of the column and the RP-HPLC line is such that residual liquids are trapped in the headspace between the end of the column support materia and the RP-HPLC coupling. It is well known in the art that a zero-head space is required in order to assure the most accurate HPLC measurements. The existence of a non-zero head space introduces errors into the HPLC analysis.
Chemical procedures and treatments performed on a sample in preparation for analysis can become tedious, particularly where repetitive chemistries must be performed and time consuming where hundreds or thousands of samples are involved. Additionally, it also creates significant opportunities for errors in measurement, and for contamination of the sample or reagents. Further, if characterization of the sample requires several different chemistries to be performed there is an increased chance of error as the technician must now identify, track, and monitor the progress of each of the required protocols. Although the present state of the art includes micro-controller interface with semi-automated apparatus, the technician must still determine which chemical procedure or protocol is to be performed on any particular sample, and key that protocol selection into the micro-controller. If the technician executes the incorrect protocol, the sample is ruined at best, or, at worst the erroneous analytical data recorded on that sample is included in the data being accumulated.
There is a need to provide an automated means for sequential, uninterrupted performance of chemistries on a plurality of samples contained within or immobilized on a plurality of sample columns with minimal human intervention and reduced risk of performing incorrect protocols.